The present invention pertains to the field of chemical fixation of hazardous waste materials, including metal-bearing materials and radionuclides and radioactive substances, in debris, soils, solid materials, sludges and materials precipitated or filtered from liquids, rendering such hazardous waste materials within a stabilized, insoluble, non-leachable, non-zeolitic and pH stable form suitable for safe and ecologically-acceptable disposal; typically regulated by the U.S. Department of Energy, the U.S. Environmental Protection Agency (xe2x80x9cUSEPAxe2x80x9d), and others. The ecologically safe state of the treated materials is not altered by exposure of the treated materials to acidic leachate, acid rain, or radioactive groundwater. In addition, the safe state of the treated materials is not altered by exposure to changing weather conditions; including rain, heat, freeze and thaw.
Various forms of hazardous wastes pose a serious threat to the environment and safe and cost efficient methods for treating and disposing of these wastes has become increasingly important.
Hazardous wastes containing excessive amounts of leachable lead are banned from land disposal. The regulatory threshold limit under Resource Conservation and Recovery Act is 5 mg/l of leachable lead as measured by TCLP (toxicity characteristic leaching procedure) test criteria, United States Environmental Protection Agency (USEPA) method 1311 (SW-846). Waste materials containing TCLP lead levels in excess of 5 mg/l are defined as lead-toxic hazardous waste and are as such restricted from land-filling under current land ban regulations. The cost of disposing lead toxic hazardous waste materials is in excess of $200.00 per ton plus the cost of transporting the hazardous material to landfills for hazardous wastes, which do not exist in every state. This makes the disposal of lead toxic hazardous waste material very expensive. Therefore, treating the lead-bearing process materials and waste streams to render them non-hazardous by RCRA definition would cut down the costs of transportation and disposal tremendously.
Conventional treatment methods for radionuclides and other radioactive substances can be categorized into three groups: 1) separation; 2) structural containment; and 3) physical stabilization/solidification. These treatment methods are complex, costly, expand volumes, and are only temporary solutions.
Various conventional methods have been tried to remove leachable, mobile radionuclides and radioactive substances from soils and other materials. Removal of contamination from soils and solid materials by leaching, centrifugation, extraction and/or washing procedures is extremely expensive and cost-prohibitive because these methods generate vast quantities of contaminated liquid wastes which require further treatment and disposal.
Conventional solidification methods based on cementation technology require up to twenty-eight (28) days curing time, increase the waste volume and may raise the pH above 12.5. USEPA defines a pH above 12.5 as hazardous. Hardened cementitious material is not conducive to retreatment in the event treatment fails obligatory confirmation testing. Solidification methods utilizing lime kiln dust, calcium carbonate and/or powdered lime for fixation are, at best, temporary solutions. Furthermore, these methods increase the waste volume and mass. A primary concern is that cementitious methods dilute the parameters of concern in the final waste matrix.
In the past, radionuclide and radioactive wastes have been temporarily stored; frequently as a liquid, a sludge, or a contaminated fine-grained solid in conjunction with contaminated soils. The art has recognized that a means must be provided for permanent disposal of these wastes, preferably as non-leachable solids, containing non-migratory radionuclides. Such solids must have certain characteristics which make the solids safe and economical for the long term (103 to 106 years) retention of radioactive isotopes.
The present invention discloses a method of treating hazardous waste materials, including metal-bearing materials and radionuclides and radioactive substances.
One embodiment of the present invention relates to a chemical treatment technology for immobilizing leachable lead in contaminated soils and solid waste materials. According to the present invention, a process for treating lead-toxic solid wastes in order to stabilize the leachable lead is disclosed, comprising the steps of. (i) mixing the solid waste with a sulfate compound, such as calcium sulfate dihydrate (gypsum powder) or sulfuric acid, having at least one sulfate ion for contacting waste particles and reacting with said leachable lead to produce a substantially insoluble lead composition, such as anglesite and/or calcium-substituted anglesite; and, (ii) mixing said solid waste and sulfate compound with a phosphate reagent, such as phosphoric acid, having at least one phosphate ion for reacting with said leachable lead to produce a substantially insoluble lead composition. The treated material from this process is substantially solid in form and passes the Paint Filter Test while satisfying the regulatory standard for TCLP lead. In all instances, application of this process has been found very reliable in meeting the treatment objectives and in consistently decreasing waste volume.
It is an object of the present invention to provide a technology for treatment of lead-containing solid waste and soil that produces an acceptably low level of leachable lead in the final product to comply with the statutory requirements of TCLP and to pass the Paint Filter Test.
Another object of the invention is to provide such a process while producing no wastewater or secondary waste streams during said process.
Still another object of the invention is to provide such a process which also causes the solid waste material to undergo a volume reduction as a result of treatment.
Yet another object of the invention is to cause fixation of the leachable lead in the solid waste that is permanent under both ordinary and extreme environmental conditions.
The present invention relates to treatment methods employed to chemically convert leachable metal in metal-bearing solid and liquid waste materials to a non-leachable form by mixing the material with one or a combination of components, for example, lime or gypsum and phosphoric acid. The solid and liquid waste materials include contaminated sludges, slurries, soils, waste waters, spent carbon, sand, wire chips, plastic fluff, cracked battery casings, bird and buck shots and tetraethyl lead contaminated organic peat and muck. The metal-hearing materials referred to herein which the present invention treats include those materials having leachable lead, aluminum, arsenic (III), barium, bismuth, cadmium, chromium (III), cooper, iron, nickel, selenium, silver and zinc. The present invention discloses a process comprising a single step mixing of one or more treatment additives, and a process comprising a two step mixing wherein the sequence of performing the steps may be reversible. The present invention provides a novel way of treating a plurality of metal-contaminated materials at a wide range of pH. The method works under acidic, alkaline and neutral conditions.
The processes of the present invention provide reactions that convert leachable metals, especially lead, into a non-leachable form which is geochemically stable for indefinite periods and is expected to withstand acid rain impacts as well as the conditions of a landfill environment.
A first group of treatment chemicals for use in the processes of the present invention includes lime, gypsum, alum, halites, Portland cement, and other similar products that can supply sulfates, halites, hydroxides and/or silicates.
A second group consists of treatment chemicals which can supply phosphate ions. This group includes products such as phosphoric acid, pyrophosphates, triple super phosphate (TSP), trisodium phosphate, potassium phosphates, ammonium phosphates and/or others capable of supplying phosphate anion when mixed with a metal-bearing process material or with a metal-toxic hazardous waste. Depending on the process material or waste (i) matrix (solid, liquid or mixture thereof), (ii) category (RCRA or Superfund/CERCLIS), (iii) chemical composition (TCLP lead, total lead level, pH) and (iv) size and form (wire fluff, shots, sand, peat, sludge, slurry, clay, gravel, soil, broken battery casings, carbon with lead dross, etc.) the metal-bearing material is mixed with one or more treatment chemicals in sufficient quantity so as to render the metal substantially non-leachable, that is, to levels below the regulatory threshold limit under the TCLP test criteria of the USEPA. For lead-bearing materials, the treatment additives render the lead below the regulatory threshold limit of 5 mg/l by the TCLP test criteria of the USEPA. The disposal of lead-hazardous and other metal-hazardous waste materials in landfills is precluded under land ban regulations.
It is an object of the present invention to provide a method of treating metal-bearing materials, contaminated soils and waste effluent, and solid wastes containing hazardous levels of leachable metal. It is a further object to provide a method which decreases the leaching of lead in lead-bearing materials to levels below the regulatory limit of 5 mg/l by TCLP test criteria.
It is another object of the present invention to provide a method to immobilize lead to leachable levels below 5 mg/l by TCLP test criteria, through the use of inexpensive, readily accessible treatment chemicals. With this method, the leachability of lead is diminished, usually allowing municipal landfill disposal which would not otherwise be permitted.
Yet another object of the present invention is to provide a treatment method for metal-bearing wastes, particularly lead-bearing wastes, which comprises a single step mixing process or a two-step process wherein the sequence of the two steps may be reversed.
Another object of the present invention is to provide a method of treating a wide variety of lead bearing process materials, wire fluff and chips, cracked battery plastics, carbon with lead dross, foundry sand, lead base paint, leaded gasoline contaminated soils, peat and muck, sludges and slurries, lagoon sediment, and bird and buck shots, in order to render the material non-hazardous by RCRA definition, and pass the EPTOX, MEP, ANS Calvet and DI Water Extract tests.
Another object of the present invention is to extend the scope for broad application in-situ as well as ex-situ on small as well as large quantities of metal-bearing process materials or generated waste streams.
The present invention provides a method which converts metal-toxic process materials and hazardous wastes into a material which has a lower leachability of metal as determined by EPA""s TCLP test. Such treated waste material can then be interned in a licensed landfill, a method of disposal only possible when the leachability of metal is diminished/reduced to levels below the regulatory threshold limit by TCLP test criteria, e.g., lead below 5 mg/l.
Another embodiment of the present invention relates to a chemical treatment process that reduces the leachability and solubility of radionuclides and other radioactive substances contained in debris, soils, sludges and solid materials (xe2x80x9cthe host materialxe2x80x9d or xe2x80x9cthe host matrixxe2x80x9d). The process for treating radionuclides and other radioactive substances employs the same methods and treatment chemicals used for treating metal-bearing hazardous waste materials. The process comprises contacting radionuclides and other radioactive substances in the host matrix with the first and second group treatment chemicals to promote recrystallization of the host material into Apatitic-structured end-products. Preferred reactants are comprised of at least one phosphate group and create mineral species of Apatitic geometric structures with reduced nuclide leachability and solubility. In the preferred embodiment, technical grade phosphoric acid (TGPA) is used in a one step process. TGPA contains sulfate as an impurity in addition to a phosphate anion source.
In one embodiment of the present invention, radionuclides and other radioactive substances in the host matrix are contacted with a treatment reagent in the form of a suspension. The suspension is formed from a first component selected from the first group of treatment chemicals and a second component selected from the second group of treatment chemicals. The first and second components can be in either the solid or liquid form or a combination of a solid and a liquid. In a preferred embodiment, a third component is included in the suspension, selected from the second group of treatment chemicals.
The present invention also provides a method of treating a contaminated material that can be either radionuclides and other radioactive substances in the host matrix, a metal-bearing material, a metal-bearing soil, a metal-bearing sludge, a waste matrix of metal-bearing material and soil or a combination thereof. The method includes the steps of contacting the contaminated material with a suspension comprising a first component and a second component to form a mixture, wherein the contaminated material contains radionuclides and other radioactive substances alone or in combination with at least one leachable metal selected from the group consisting of lead, aluminum, arsenic (III), barium, bismuth, cadmium, chromium (III), copper, iron, nickel, selenium, silver and zinc, wherein the first component supplies at least one member from the group consisting of sulphates, halides, halites, silicates and calcium oxide, and wherein the second component supplies at least one phosphate anion; and curing the mixture for a period of time to form a cured material; wherein the concentration of leachable radioactive substances in the contaminated material so treated is decreased and non-leachable solid materials are formed and the leachable metal level in the cured material is below 5.0 mg/l.
The Apatite-structure ((AB)5(PO4)3Z) is preferred since the anion Z position is usually a halogen or a hydroxyl, both active scavengers of cations. The unique properties of the Apatitic-structure, (AB)5(XO4)3Z, are key to this invention. Just as low-temperature Apatite is nature""s ion-prison in the biological/biosphere environment and high-temperature Apatite is natures ion-prison in the pegmatites/igneous lithosphere environment, Apatites can do the same in man-made (unnatural/synthetic) radioactive environments. The supplementary problem of metamict lattice disruptions, from the generation of excess heat and ion-cannon recoil damage by radioactive decay, is also self-resolved in Apatites.
Both low-temperature and high-temperature Apatitic-structures are self-healing and non-leaching. In one embodiment of the present invention, the flow of normal groundwater through the treated material should be encouraged since the groundwater will disperse the build-up of heat and eliminate the requirement for costly cooling of monolithic encasement structures. In another embodiment of the present invention, treated material contacted with groundwater contaminated with radionuclides and radioactive substances reduces the radioactive level of the ground water.
Natural scavenging of Lanthanides and Actinides by Apatitic-structure phosphate-complexing phases is well-documented from research conducted in connection with the mining of oceanic deposits throughout the world to produce phosphate products. To date, more than 300 Apatite mineral species have been classified by geologists.
Substitution within Apatites are extremely complex. Many require a charge-compensating mechanism that can be grossly estimated from ionic radii and coordination numbers. Common substitution mechanisms noted are as follows: 1) simple within-site substitutions; 2) coupled substitutions involving chemically similar cations; 3) substitutions involving large cations, such as Cs, with smaller cations; 4) substitutions involving cation vacancies; 5) substitutions coupling specific cations with specific anions; 6) substitutions involving anions; 7) substitutions involving anion vacancies; and 8) substitutions involving a change in valence.
From the structural and compositional studies of natural and synthetic Apatites, it is known that Apatites are complex geological structures. The present invention has found that Apatites can sustain a great variety of substitutions following the general formula (AB)5(XO4)3Z, [sometimes written, (AB)10(XO4)6Z2], wherein:
A=Coordination Number 7 thru 12, most commonly 9. Cations smaller than Mn+2 are to small for an 8 coordination number, unless combined with a larger cation.
=Ca, Sr, Mn, Pb, Mg, Ba, Zn, Cd, Fe, Ni, Co, Sn, Eu, Cu, and Be among divalent elements.
=Na, K, Rb, Ag, Cs and possibly Li among monovalent elements.
=Al, Fe, Y, rare earth elements (REE) except Eu and Ce, Bi and possibly Nb, Sb and Ti among trivalent elements,
=U, Pb, Th, Zr, Ce, Transuranics and possibly TI among quadrivalent elements.
=[ ] minor lattice vacancies.
B=Coordination Number 6 thru 9, most commonly 8. Cations smaller than W+6 are small for 6 coordination number and those larger than Zr+4 are too large.
=Ca, Sr, Mn, Pb, Mg, Ba, Zn, Cd, Fe, Ni, Co, Sn, Cu, and Be among divalent elements.
=Na, K, Rb, Ag, Li possibly among monovalent elements.
=Al, Fe, Sc, Sb, Y, Eu and Ce REE, Nb, Bi and possibly Ta among trivalent elements.
=Si, Mn, Ti, Mo, W, Sn, U, Th, Zr, C among quadrivalent elements.
=Actinide ion species conforming to Metal.O2 (especially UO2).
=[ ] minor lattice vacancies.
XO4=PO4, SiO4, SO4, AsO4, VO4, CrO4, BeO4, MoO4, CO3, CO3F, WO4, MnO4, CO3OH, BO4, AlO4, Fe3O4, possibly GeO4, and SeO4.
Z=F, OH, Cl, Br, I, O and [ ] minor lattice vacancy in structure of defective Apatites.
Element 43xe2x80x94Technetium is effected by the process with leachability greatly reduced; however, its positioning within the Apatitic-structure has not been determined with certainty.
Additionally, the radius ratios among A, B and XO4 components, and their respective coordination number, can have a strong influence on the Apatite-structure. Problems occur when an element""s ionic radius is small for A and large for B; therefore, a single site cannot be considered alone and a partitioning between A and B sites is proposed. The partitioning is extremely difficult to predict since the amounts involved may be very minor as well as promoting localized crystal disorder.
In its simplest and most efficient form, the current invention provides for the addition of at least one member selected from a first group of treatment chemicals that can supply sulfates, halides, hydroxides and/or silicates and at least one member selected from a second group of treatment chemicals that can supply phosphate ions to material consisting of, or containing, radionuclides and other radioactive substances. Technical grade phosphoric acid (xe2x80x9cTGPAxe2x80x9d) that contains up to 70% (by weight) phosphate (as P2O5) and sulfate (SO4xe2x88x922), typically as sulfuric acid in the range of 2.5% to 7% (by weight) as an impurity, is a source of both a sulfate ion and a phosphate ion and can, therefore, be used as a single reactant. The addition of water at any point in the process aids in the dispersion of the TGPA throughout the host matrix. As the TGPA disperses and permeates through the matrix and during the course of subsequent reactions, the leachability and solubility of radionuclides and other radioactive substances is reduced. Supplemental mechanical or physical mixing can also be employed to enhance the contact of the TGPA with the leachable species in the host material.
As a true chemical process, an object of the invention relies on molecular bonding and crystal nucleation principles to reduce nuclide solubility and to create conditions suitable for matrix volume reduction resulting, in part, from the dehydration properties of the treatment chemicals. When TGPA is utilized, molecular rearrangement and minimized addition of treatment agents is characteristic of the invention and supplemental buffering agents or traditional strength enhancement physical-binding additives typical of physically stabilized mixtures are not required. The end-product of the invention is a material that contains no free liquids and produces no supernatant wastewater or secondary waste streams. A further loss of water weight is achieved by capillary drying and evaporation which also contribute to volume reduction. Some volume reduction can be attributed to acidic carbonate destruction, especially those not incorporated into the Apatitic structures. The end product is friable and can be handled with traditional earth-moving equipment, as it is not monolithic in form.
Moreover, the end-product can be made to have enhanced geotechnical properties without compromising the chemistry of the nuclide leachability/solubility reduction. The addition of water, either to suppress dust or due to rainfall, and excavation or other material handling activities do not affect the nuclide leachability or solubility of the end-product.
Another object of the invention is to increase the level of protection offered by disposal facility designs engineered specifically to control, isolate, or contain material characterized with leachable radionuclides; and to minimize the migration of radionuclides and other radioactive substances from material that is accessed by the percolation of rain and surface waters, and/or the intrusion and flow-through of groundwater or leachate that can act as an ion-carrier. When groundwater contaminated with radionuclides and radioactive substances are contacted with materials treated by the present invention, the radioactive level of the groundwater will be reduced. The radionuclides and radioactive substances in the groundwater react with the phosphate compounds and sulfate compounds in the treated materials to form geochemically stable Apatite-structures.
A further object of the present invention is the addition of liquid or solid reagents to a solid material or sludge without creating secondary byproducts or separable streams. Another object of the present invention is to engage and employ preexisting carbonates, borates, sulfates, and/or silicates within the matrix at the time of phosphate anion addition so that they contribute to the formation of Apatitic-structures that reduce nuclide leachability and solubility and host matrix volume. An additional objective of the invention is the immediate initiation of process reactions upon the contacting of phosphate anion with the leachable or soluble species, without the separation of nuclides or other byproducts from the matrix. Another objective is the in situ or ex situ application of process reagents to nuclide material; wherein fixation of the nuclides is permanent under both ordinary and extreme environmental conditions. Still another object of the invention is the use of acidity to enhance dissassociation of semi-soluble species so that problematic nuclides are freed to nucleate within the Apatite crystals. These and other objects will be apparent from the detailed description of the invention set forth below.
The invention may be more fully understood with reference to the accompanying drawings and the following description of the embodiments shown in those drawings. The invention is not limited to the exemplary embodiments but should be recognized as contemplating all modifications within the skill of an ordinary artisan.